The recent introduction of WiMAX technology promises to further increase the proliferation of wirelessly-equipped devices. WiMAX (Worldwide Interoperability for Microwave Access) is an Institute of Electrical and Electronics Engineers (IEEE) standard, designated 802.16, with the 802.16e being the current version of the standard (the terms “IEEE 802.16,” “IEEE 802.16e,” and “WiMAX” may be used interchangeably herein). WiMAX provides a robust mechanism for wireless communication between base stations and subscriber stations. In particular, WiMAX is designed to provide fixed, portable or non-line-of-sight service with a potential range of 6 miles, a potential bandwidth on the order of 40 megabits per second, and superior quality of service and security.
WiMAX chipsets that provide for communication in accordance with the WiMAX protocol are becoming increasingly prevalent as standard or optional equipment not only in traditional wireless communications devices, such as cellular phones and personal digital assistants, but also in devices that, heretofore, were not used for access to telephony networks. These devices include portable music players, entertainment devices such as game players, automobiles, domestic appliances and so on. It is expected that by the year 2009 there will be in excess of 100 million devices in use that have WiMAX chipsets in them. Thus, a virtual explosion of the number of WiMAX devices is expected to occur in the near future.
In a WiMAX network, users may connect to a WiMAX base station using different timing characteristics and/or power levels. For example, characteristics of a device's connection such as timing, power, and/or transmit frequency offset may be adjusted depending on the location of the user and the user's distance from a base station, as well as other factors. To make such adjustments for a connection, WiMAX defines various ranging processes.
Generally, WiMAX involves four ranging processes: initial ranging, periodic ranging, bandwidth requests, and handoff ranging. Initial ranging may be used to make adjustments prior to establishing network connectivity. Periodic ranging may be similar to initial ranging, but occurs after a connection is established, and helps periodically adjust characteristics of the connection (for example, if a user changes location or network conditions change, periodic ranging may be used to update the parameters of the user's connection). A bandwidth request may be sent when a user desires more or less bandwidth. Lastly, handoff ranging requests may help transfer a WiMAX connection from one WiMAX base station to another, so that a user can freely roam between coverage areas of different base stations.
To initiate these ranging processes, a WiMAX device may send ranging requests. According to IEEE 802.16e, there are 256 different ranging codes that can be used for ranging requests. Each of the 256 ranging codes takes the form of a 144-bit Code Division Multiple Access (CDMA) code. Of the 256 ranging codes, 64 are assigned to each ranging process (e.g., 64 initial ranging codes, 64 periodic ranging codes, etc.). Alternatively, some vendors are building chipsets implementing a smaller fixed number of ranging codes for each ranging process. For example, a chipset might allocate 32 ranging codes for handoff ranging requests, 20 ranging codes for bandwidth requests and four codes for both initial and periodic ranging. In any event, with a fixed set of ranging codes available to request each type of ranging process, a base station receiving a ranging request can identify which ranging process is being requested based on the ranging code.
When a WiMAX base station receives a ranging request, the base station may send the client device a ranging response that tells the client device to adjust its power and timing in some manner. After the client device makes the adjustment(s) specified in the ranging response, the client device sends a new initial ranging request to the base station using the adjusted parameters. This back and forth process will continue until the base station is satisfied with the power and timing characteristics for the connection.